Substrate for Transparent Electrodes

ABSTRACT

One object of the present invention is to provide a transparent electrode substrate with an ITO film formed thereon, used for example as the transparent electrode plate in a dye sensitized solar cell, for which the electrical resistance does not increase even when exposed to high temperatures of 300° C. or higher. In order to achieve the object, the present invention provides a substrate for a transparent electrode, wherein two or more layers of different transparent conductive films are formed on a transparent substrate, and an upper layer transparent conductive film has a higher heat resistance than that of a lower layer transparent conductive film.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a transparent electrode substrate foruse in transparent electrode plates and the like of devices such asliquid crystal display elements and solar cells, and in particular to atransparent electrode substrate with increased heat resistance.

2. Description of the Related Art

Transparent electrode plates of liquid crystal display elements andsolar cells and the like typically use a transparent substrate such asglass, on which is provided a thin film of thickness 50 to 1,000 nm ofindium oxide doped with several percent of tin, known as an indium tinoxide film (hereafter abbreviated as an ITO film).

However, although this ITO film has excellent transparency and a highlevel of conductivity, it suffers from deteriorating heat resistance attemperatures over 300° C.

Namely, when ITO films are exposed to a high temperature of 300° C. orhigher, the electrical resistance of the ITO film increases more thanthree times, and the conductivity decreases markedly. It is thought thatthe reason for this behavior that on heating, oxygen from the atmospherebonds to a portion of the oxygen vacant structures within the ITO film,reducing the oxygen vacancies which functions as a passage forelectrons.

Consequently, if this type of transparent electrode plate with an ITOfilm formed thereon is used, for example, to make a dye sensitized solarcell, then a paste formed from fine oxide powder such as titanium oxideis coated on the surface of the ITO film of the transparent electrodeplate, and the paste is calcinated at a temperature of 400 to 600° C. toform porous oxide semiconductor film. However, during this process, theconductivity of the ITO film of the transparent electrode platedeteriorates markedly. As a result the photoelectric conversionefficiency of the dye sensitized solar cell also deteriorates.

For example, Japanese Unexamined Patent Applications, First PublicationNos. Hei 7-249316 and Hei 9-063954 disclose the conventional transparentelectrode plate.

Accordingly, an object of the present invention is to provide atransparent electrode substrate with an ITO film formed thereon, usedfor example as the transparent electrode plate in a dye sensitized solarcell, for which the electrical resistance does not increase even whenexposed to high temperatures of 300° C. or higher.

SUMMARY OF THE INVENTION

In order to achieve the above object, the present invention provides asubstrate for a transparent electrode, wherein two or more layers ofdifferent transparent conductive films are formed on a transparentsubstrate, and the upper layer transparent conductive film has a higherheat resistance than the lower layer transparent conductive film.

According to the substrate for a transparent electrode, even if thissubstrate for a transparent electrode is exposed to high temperatures of300° C. or higher, the electrical resistance does not increase, and thetransparency does not deteriorate.

In the substrate for a transparent electrode, it is preferable for theincrease in the electrical resistance of the upper layer transparentconductive film on heating at 300 to 700° C. to be suppressed to anincrease of no more than two times, and for the increase in theelectrical resistance of the lower layer transparent conductive film onheating at 300° C. or higher to be at least 1.5 times.

In the substrate for a transparent electrode, it is also preferable fortwo or more layers of different transparent conductive films to beformed on a transparent substrate, for at least one of the layers otherthan the uppermost layer to be an ITO film, and for a transparentconductive film for which the increase in the electrical resistance onheating at 300 to 700° C. is suppressed to no more than two times to beformed on top of the ITO film.

In the substrate for a transparent electrode, it is also preferable forthe transparent conductive film laminated on top of the ITO film to beprepared by a spray pyrolysis deposition method (hereafter referred toas a SPD method).

In the substrate for a transparent electrode, it is also preferable forthe transparent conductive film laminated on top of the ITO film to beformed consecutively and immediately after the formation of the ITOfilm.

According to the substrate for a transparent electrode, since during theformation of a highly heat resistant transparent conductive filmdifferent from an ITO film on top of the ITO film, by forming the heatresistant film consecutively and immediately after the formation of theITO film, the ITO film does not undergo oxidation deterioration duringthe heat resistant film formation operation, and no loss occurs in theoriginal high conductivity and transparency of the ITO film. As aresult, a transparent electrode substrate with superior heat resistance,conductivity and transparency can be obtained.

In the substrate for a transparent electrode, it is also preferable forat least one transparent conductive film other than the ITO film tocomprise one or more transparent conductive films selected from a groupconsisting of fluorine doped tin oxide (hereafter referred to as a FTOfilm), antimony doped tin oxide (hereafter referred to as a ATO film),tin oxide, fluorine doped zinc oxide, aluminum doped zinc oxide, galliumdoped zinc oxide (hereafter referred to as a GZO film), boron doped zincoxide, and zinc oxide.

In addition, in order to achieve the above object, the present inventionprovides a substrate for a transparent electrode wherein an ITO film isprovided on a transparent substrate, a FTO film is provided on this ITOfilm, and the thickness of the ITO film is 100-1000 nm.

According to the substrate for a transparent electrode, it is possibleto provide a substrate for a transparent electrode having hightransparency.

In the substrate for a transparent electrode, it is preferable for thethickness of the FTO film to be 30-350 nm. In addition, the thickness ofthe FTO film is more preferably to 100-350 nm, and most preferably to150-350 nm.

According to the substrate for a transparent electrode, it is possibleto provide a substrate for a transparent electrode having improved heatresistance in which resistance is not increased by heating at 250-700°C.

In addition, in order to achieve the above object, the present inventionprovides a method of producing a substrate for a transparent electrode,wherein the film formation temperature of an ITO film is 280° C. orhigher when producing the substrate for a transparent electrode byproviding the ITO film on a transparent substrate by means of a SPDmethod and by providing a FTO film on the ITO film.

Furthermore, in order to achieve the above object, the present inventionprovides another method of producing a substrate for a transparentelectrode, wherein the film formation temperature of a FTO film is360-440° C. when producing the substrate for a transparent electrode byproviding an ITO film on a transparent substrate by means of a SPDmethod and by providing the FTO film on the ITO film.

When carrying out film formation of the ITO film and FTO film by a SPDmethod, by setting the film formation temperature of the ITO film to280° C. or higher, a low-resistance transparent conducting film can beformed, and by setting the film formation temperature of the FTO film to360-440° C., a transparent conducting film having high heat resistancecan be formed without increasing the resistance even if heated at 300°C. or higher.

In addition, in order to achieve the above object, the present inventionprovides a photoelectric conversion element using the substrate for atransparent electrode as a transparent electrode plate.

Furthermore, in order to achieve the above object, the present inventionprovides a dye sensitized solar cell using the substrate for atransparent electrode as a transparent electrode plate.

According to the dye sensitized solar cell, since it uses thetransparent electrode substrate described above as a transparentelectrode plate, and consequently even when heated to a high temperatureduring the calcination of an oxide semiconductor porous film, the lowelectrical resistance of the transparent electrode plate is maintained,enabling the production of a solar cell with a high degree ofphotoelectric conversion efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional diagram showing an example of asubstrate for a transparent electrode according to the presentinvention.

FIG. 2 is a schematic cross-sectional diagram showing an example of adye sensitized solar cell according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As follows is a more detailed description of the present invention basedon a series of embodiments.

FIG. 1 is a diagram showing one example of a substrate for a transparentelectrode according to the present invention. In the figure, numeral 1represents a transparent substrate. This transparent substrate 1 is aglass plate of thickness 0.3 to 5 mm formed from a glass such as sodaglass, heat resistant glass or quartz glass.

A first transparent conductive film comprising an ITO film 2 is formedon one surface of the glass plate of the transparent substrate 1. ThisITO film 2 is a thin film formed by a thin film formation means such asa sputtering method, CVD method, and SPD method. This ITO film 2 hasgood conductivity and transparency, and if the film thickness becomesthick, the conductivity as a transparent conducting film improves, whichis preferable. However, the transparency will decrease, and the filmthickness should be 100-1000 nm. Furthermore, this ITO film 2 has a lowheat resistance, and the electrical resistance due to heating at 300° C.or higher increases to at least 1.5 times.

A FTO film (hereafter referred to as a FTO film) 3 as a secondtransparent conductive film is formed on top of the ITO film 2. This FTOfilm 3 is formed from tin oxide doped with several ppm of fluorine, andis a thin film which displays excellent heat resistance and chemicalresistance. This FTO film 3 is highly heat resistant and displays anincrease in electrical resistance which is suppressed to no more than 2times on heating at 300 to 700° C.

The thickness of this FTO film 3 must be at least 30 nm in order toprotect the ITO film 2 underlayer. However, if it becomes too thick, theoverall transparency decreases, and the upper limit should be 350 nm.The film thickness of this FTO film 3 largely determines the heatresistance as a transparent conducting film.

For example, if the film thickness is set to 30-350 nm, the conductivitydoes not decrease even due to heating at a temperature of 250-700° C.for one hour. If the film thickness is set to 100-350 nm, theconductivity does not decrease even due to heating at a temperature of450-700° C. for one hour. If the film thickness is set to 150-350 nm,the conductivity does not decrease even due to heating at a temperatureof 650-700° C. for one hour.

Therefore, it is possible to adjust the film thickness depending on theheat resistance which is required to a substrate for a transparentelectrode.

The FTO film 3 can be formed using a thin film formation technique suchas a SPD method, a sputtering method, or a CVD method, although ofthese, a SPD method is preferred.

This SPD method is a variety of thin film formation technique wherein araw material compound solution is sprayed onto a heated substrate, apyrolysis reaction is initiated on the substrate generating fineparticles of an oxide, and these fine particles of oxide are depositedon the surface of the substrate. This type of SPD method can be used forforming a FTO film by using a solution of a tin oxide such as tin (II)oxide and a fluorine compound such as ammonium fluoride as the rawmaterial compound solution.

Furthermore, the formation of the FTO film of the second transparentconductive film 3 must be conducted immediately after the formation ofthe ITO film 2 of the first transparent conductive film. The reason forthis requirement is because if the ITO film 2 is exposed to a hightemperature of 450 to 550° C., then the film will oxidize within a veryshort time period of only 2 to 3 minutes, causing a reduction inconductivity. Therefore, if the glass substrate 1 with the ITO film 2formed thereon is heated for a second time from room temperature to the500 to 600° C. required for formation of the FTO film 3, the ITO film 2will deteriorate during this heating period, before the FTO film 3 ofthe second transparent conductive film can be formed.

As a result, it is necessary to spray the raw material compound solutionfor the FTO film 3 onto the glass plate 1 immediately after theformation of the ITO film 2, while the temperature of the glass plate 1is still at approximately 400 to 500° C., and form the FTO film 3 by SPDmethods before the ITO film 2 can begin to deteriorate. Accordingly, thespraying of the raw material compound solution used for forming the FTOfilm 3 of the second transparent conductive film must be commencedwithin 1 to 3 minutes of completing the formation of the ITO film 2 ofthe first transparent conductive film.

By employing this type of consecutive and immediate film formationoperation, the surface of the ITO film 2 can be covered with the highlyheat resistant FTO film 3 before the ITO film 2 undergoes oxidationdeterioration. In cases in which a thin film formation method other thenthe aforementioned SPD method is employed in the consecutive filmformation operation, the temperature during film formation of the FTOfilm 3 can still not be reduced to a temperature below 300° C., andconsequently the same time restriction applies.

Furthermore, a method is adopted which sets the film formationtemperature of the ITO film 2 to 280° C. or higher, preferably 280-460°C., when producing a substrate for a transparent electrode by providingthe ITO film 2 on the transparent substrate 1 by means of a SPD methodand subsequently providing the FTO film 3 on this ITO film 2 by means ofthe SPD method. Moreover, a method is adopted which sets the filmformation temperature of the FTO film 3 to 360-440° C.

By setting the film formation temperature of the ITO film 2 to 280° C.or higher as described above, it is possible to form a low-resistancetransparent conducting film with high conductivity. Furthermore, bysetting the film formation temperature of the FTO film 3 to 360-440° C.,it is possible to form a transparent conducting film having good heatresistance without increasing the resistance even if heating is carriedout at 450° C. for one hour.

According to a transparent electrode substrate of this type ofconstruction, the second transparent conductive film which is a FTO film3 and which displays superior heat resistance and for which theelectrical resistance does not increase appreciably even on exposure tohigh temperatures, is laminated on top of the first transparentconductive film 2 which is an ITO film, and covers the ITO film 2, andconsequently even when exposed to high temperatures of 300° C. orhigher, the ITO film 2 does not oxidize and no loss occurs in the highconductivity of the ITO film 2.

Furthermore, the FTO film of the second transparent conductive film 3has a higher electrical resistance and a poorer transparency than an ITOfilm, but because the thickness of this FTO film 3 may be keptreasonably thin, the electrical resistance and the transparency of theoverall laminated film structure do not deteriorate appreciably.

In addition, FTO films also offer a high degree of chemical resistance,and consequently yield an overall laminated film structure with a highdegree of chemical resistance.

Furthermore, by forming the FTO film 3 immediately after the formationof the ITO film 2, oxidation deterioration of the ITO film 2 during thefilm formation operation for the FTO film 3 can be prevented, and noloss occurs in the high conductivity of the ITO film 2.

In addition, in the present invention, other films with similarcharacteristics to a FTO film can also be used for the secondtransparent conductive film 2, including transparent conductive films ofantimony doped tin oxide (ATO), tin oxide (TO), fluorine doped zincoxide (FZO), aluminum doped zinc oxide (AZO), gallium doped zinc oxide(GZO), boron doped zinc oxide (BZO) or zinc oxide (ZO), of filmthickness from 30 to 500 nm. These transparent conductive films offer asimilar high level of heat resistance to the FTO film 3, and display anincrease in electrical resistance which is suppressed to no more than 2times on heating at 300 to 700° C.

Furthermore, a third transparent conductive film and a fourthtransparent conductive film and beyond, can also be formed on top of thesecond transparent conductive film 3, forming a plurality of layers ofthe aforementioned transparent conductive films other than the ITO film.

In addition, a transparent conductive film other than an ITO film mayalso be formed directly on top of the transparent substrate 1, with anITO film then formed on top of this transparent conductive film, and atransparent conductive film other than an ITO film, such as a FTO filmor the like, then formed on top of the ITO film.

Furthermore, the form of the transparent substrate is not restricted toa flat plate. Moreover, a substrate for a transparent electrodeaccording to the present invention is, of course, not restricted to useas a transparent electrode plate for a dye sensitized solar celldescribed above, and can also be used for other devices such asphotoelectric conversion elements which are exposed to high temperaturesof 300° C. or higher, either during production or in subsequent use.

FIG. 2 is a diagram showing one example of a dye sensitized solar cell,representing a specific example of a photoelectric conversion element ofthe present invention.

In FIG. 2, numeral 11 represents a transparent electrode plate. Thistransparent electrode plate 11 is formed from a transparent electrodesubstrate as described above, and comprises, for example, a transparentsubstrate 12 such as a glass plate on which is laminated an ITO film 13and a FTO film 14.

On top of the FTO film 14 of this transparent electrode plate 11 isformed an oxide semiconductor porous film 15. This oxide semiconductorporous film 15 is a porous film of thickness 1 to 50 μm μm constructedof interconnected fine particles of a metallic oxide which displayssemiconductivity such as titanium oxide, tin oxide, tungsten oxide, zincoxide, zirconium oxide or niobium oxide, with the interior of the filmcontaining countless fine vacancies, the surface comprising fineundulations, and with the internal fine vacancies supporting aphotosensitized dye.

Formation of this oxide semiconductor porous film 15 is achieved by amethod in which a colloidal liquid, a paste, or a dispersion containingdispersed fine particles of the aforementioned metal oxide of averageparticle diameter 5 to 50 nm is applied to the surface of the FTO film14 of the transparent electrode plate 11 using an application methodsuch as screen printing, ink jet printing, roll coating, doctor coating,spin coating, spray coating or bar coating, and is subsequently baked ata temperature of 400 to 600° C.

Furthermore, suitable examples of photosensitized dyes include rutheniumcomplexes incorporating ligands such as bipyridine structures orterpyridine structures, metal complexes of porphyrins or phthalocyanine,and organic dyes such as eosin, rhodamine and merocyanine, and byimpregnating the fine cavities within the oxide semiconductor porousfilm 15 with an aqueous solution or an alcohol solution of this type ofdye and performing subsequent drying, the dye is supported in thecavities.

In FIG. 2, numeral 16 represents a counter electrode. This counterelectrode 16 may comprise a conductive substrate such as a metal plate,a non-conductive substrate such as a glass plate with a conductive filmof platinum, gold or carbon or the like formed thereon using a techniquesuch as vapor deposition or sputtering, or an electrode formed byapplying a chloroplatinic acid solution to a substrate, and then heatingthe electrode to form a platinum film.

An electrolyte formed from a nonaqueous solution incorporating a redoxpair such as iodine and iodide ions is used to fill the gap between theaforementioned oxide semiconductor porous film 15 and the counterelectrode 16, forming an electrolyte layer 17.

In a dye sensitized solar cell of this construction, if light such assunlight enters from the side of the transparent electrode plate 11,then an electromotive force develops between the transparent electrodeplate 11 and the counter electrode 16, and electrons flow from thetransparent electrode plate 11 to the counter electrode 16, producingpower generation.

According to this type of dye sensitized solar cell, because theuppermost layer of the transparent electrode substrate which forms thetransparent electrode plate 11 is a highly heat resistant FTO film 14,even during the heating required for the baking of the oxidesemiconductor porous film 15, the resistance does not increasesignificantly, and the low electrical resistance required for thetransparent electrode plate 11 is maintained, and as a result, thephotoelectric conversion efficiency of the solar cell does notdeteriorate.

In a dye sensitized solar cell of the present invention, the electrolytelayer 17 formed from the electrolyte comprising a nonaqueous solutionincorporating a redox pair can either employ a charge transfer layercomprising a solid inorganic p-type semiconductor such as copper iodideor copper thiocyanate, or alternatively, this charge transfer layer canemploy a hole transport layer. By using such a hole transport layer,volatilization and leakage of the electrolyte can also be prevented.

As follows is a description of a series of specific examples. Theexamples presented comprise a glass plate onto which an ITO film, and aFTO film, an ATO film or a TO film are formed using a SPD method.

Example 1 1. Preparation of a Raw Material Compound Solution for an ITOFilm

5.58 g of indium (III) chloride tetrahydrate and 0.23 g of tin (II)chloride dihydrate were dissolved in 100 ml of ethanol, yielding an ITOfilm raw material compound solution.

2. Preparation of a Raw Material Compound Solution for a FTO Film

0.701 g of tin (IV) chloride pentahydrate was dissolved in 10 ml ofethanol, a saturated aqueous solution of 0.592 g of ammonium fluoridewas added, and the mixture was placed in an ultrasonic washer forapproximately 20 minutes to achieve complete dissolution, yielding a FTOfilm raw material compound solution.

Subsequently, the surface of a heat resistant glass plate of thickness 2mm was subjected to chemical cleaning, and the glass plate was thendried, placed in a reaction vessel and heated using a heater. When theheating temperature of the heater had reached approximately 450° C., theITO film raw material compound solution was sprayed onto the plate for25 minutes through a nozzle with a bore diameter of 0.3 mm and at apressure of 0.06 MPa, with the nozzle separated from the glass plate bya distance of 400 mm.

Following spraying of the ITO film raw material compound solution, twominutes were allowed to elapse (during this period, ethanol was sprayedcontinuously onto the glass substrate surface in order to suppress anyincrease in the surface temperature of the substrate), and when theheating temperature of the heater reached 530° C., the FTO film rawmaterial compound solution was sprayed onto the surface under the sameconditions, for a period of 2 minutes and 30 seconds.

Through the above processes, an ITO film of thickness 530 nm and a FTOfilm of thickness 170 nm were formed on the heat resistant glass plate,yielding a transparent electrode plate according to the presentinvention.

For the purposes of comparison, identical heat resistant glass platesand the same operations were used to form a transparent electrode platecomprising only an ITO film of thickness 530 nm, and a transparentelectrode plate comprising only a FTO film of thickness 180 nm.

These three different types of transparent electrode plate were placedin a heating furnace and heated, either at 450° C. for one hour in air,or at 450° C. for 2 two hours in air, and the variation in the sheetresistance, the specific resistivity, and the transparency were thenevaluated. Measurements of electrical resistance were performed usingthe four terminal method, and measurements of transparency wereperformed using an ultraviolet-visible spectrophotometer at wavelengthsof 500 nm and 600 nm.

The results are shown in Table 1 through Table 3. Table 1 shows the dataprior to heating, Table 2 shows the data for the transparent electrodeplate following heating at 450° C. for one hour in air, and Table 3shows the data for the transparent electrode plate following heating at450° C. for two hours in air.

TABLE 1 Sheet Film Specific Transmittance Transmittance resistancethickness resistivity at 500 nm at 600 nm (Ω/□) (nm) (Ω · cm) (%) (%)ITO film 4.9 530 2.6 × 10⁻⁴ 96 91 FTO film 48 180 8.6 × 10⁻⁴ 91 97 FTOand ITO 3.3 700 2.3 × 10⁻⁴ 84 86 films

TABLE 2 Sheet Film Specific Transmittance Transmittance resistancethickness resistivity at 500 nm at 600 nm (Ω/□) (nm) (Ω · cm) (%) (%)ITO film 18 530 9.5 × 10⁻⁴ 90 84 FTO film 48 180 8.6 × 10⁻⁴ 92 96 FTOand ITO 3.3 700 2.3 × 10⁻⁴ 88 87 films

TABLE 3 Sheet Film Specific Transmittance Transmittance resistancethickness resistivity at 500 nm at 600 nm (Ω/□) (nm) (Ω · cm) (%) (%)ITO film 18 530 9.5 × 10⁻⁴ 90 85 FTO film 48 180 8.6 × 10⁻⁴ 91 96 FTOand ITO 3.3 700 2.3 × 10⁻⁴ 88 87 films

From the results shown in Table 1 through Table 3 it is evident that inthe transparent electrode plate with a FTO film laminated on top of theITO film, there is no fluctuation in electrical resistance and nodeterioration in transparency, even after heating for one or two hoursat 450° C. in air.

Next, dye sensitized solar cells of the structure shown in FIG. 2 wereprepared using each of the three types of transparent electrode platesfrom the above examples.

Formation of the oxide semiconductor porous film 15 involved dispersingfine particles of titanium oxide with an average particle diameter of230 nm in acetonitrile to form a paste, application of this paste to atransparent electrode 11 using a bar coating method to form a film ofthickness 15 μm, and then drying of the paste followed by calcinating at450° C. for one hour. A ruthenium dye was then supported in this oxidesemiconductor porous film 15.

In addition, a conductive substrate comprising an ITO film and a FTOfilm laminated on top of a glass plate was used as the counter electrode16, and an electrolyte solution formed from a nonaqueous solution ofiodine and iodide was used as the electrolyte layer 17.

The planar dimensions of the dye sensitized solar cells prepared in thismanner were 25 mm×25 mm.

Each of these dye sensitized solar cells was irradiated with artificialsunlight (AM 1.5), and the resulting power generation efficiency wasdetermined.

The results showed that for the solar cell using a transparent electrodeplate comprising both an ITO film and a FTO film, the power generationefficiency was 5.4%, whereas the result for the solar cell using atransparent electrode plate with only an ITO film was 2.7%, and theresult for the solar cell using a transparent electrode plate with onlya FTO film was 3.8%.

Example 2 1. Preparation of a Raw Material Compound Solution for an ITOFilm

5.58 g of indium (III) chloride tetrahydrate and 0.23 g of tin (II)chloride dihydrate were dissolved in 100 ml of ethanol, yielding an ITOfilm raw material compound solution.

2. Preparation of a Raw Material Compound Solution for an ATO Film

0.701 g of tin (IV) chloride pentahydrate and 0.09 g of antimonychloride was dissolved in 10 ml of ethanol, yielding an ATO film rawmaterial compound solution.

Using this ITO film raw material compound solution and this ATO film rawmaterial compound solution, and employing the same sequence as theexample 1, an ITO film of thickness 380 nm and an ATO film of thickness170 nm were formed on a heat resistant glass plate, yielding atransparent electrode plate according to the present invention.

For the purposes of comparison, identical heat resistant glass platesand the same operations were used to form a transparent electrode platecomprising only an ITO film of thickness 380 nm, and a transparentelectrode plate comprising only an ATO film of thickness 170 nm.

These three different types of transparent electrode plate were placedin a heating furnace and heated, either at 450° C. for one hour in air,or at 450° C. for 2 two hours in air, and the variation in the sheetresistance, the specific resistivity, and the transparency were thenevaluated. Measurements of electrical resistance were performed usingthe four terminal method, and measurements of transparency wereperformed using an ultraviolet-visible spectrophotometer at wavelengthsof 500 nm and 600 nm.

The results are shown in Table 4 through Table 6. Table 4 shows the dataprior to heating, Table 5 shows the data for the transparent electrodeplate following heating at 450° C. for one hour in air, and Table 6shows the data for the transparent electrode plate following heating at450° C. for two hours in air.

TABLE 4 Sheet Film Specific Transmittance Transmittance resistancethickness resistivity at 500 nm at 600 nm (Ω/□) (nm) (Ω · cm) (%) (%)ITO film 4.6 380 1.8 × 10⁻⁴ 85 95 ATO film 1.5 × 10² 170 2.5 × 10⁻³ 8390 ATO and 5.3 550 2.9 × 10⁻⁴ 83 91 ITO films

TABLE 5 Sheet Film Specific Transmittance Transmittance resistancethickness resistivity at 500 nm at 600 nm (Ω/□) (nm) (Ω · cm) (%) (%)ITO film 18 380 6.8 × 10⁻⁴ 91 85 ATO film 2.3 × 10² 170 3.9 × 10⁻³ 83 90ATO and 6.4 550 3.5 × 10⁻⁴ 83 92 ITO films

TABLE 6 Sheet Film Specific Transmittance Transmittance resistancethickness resistivity at 500 nm at 600 nm (Ω/□) (nm) (Ω · cm) (%) (%)ITO film 20 380 7.6 × 10⁻⁴ 92 87 ATO film 2.6 × 10² 170 4.4 × 10⁻³ 83 90ATO and 6.9 550 3.8 × 10⁻⁴ 84 92 ITO films

Example 3 1. Preparation of a Raw Material Compound Solution for an ITOFilm

5.58 g of indium (III) chloride tetrahydrate and 0.23 g of tin (II)chloride dihydrate were dissolved in 100 ml of ethanol, yielding an ITOfilm raw material compound solution.

2. Preparation of a Raw Material Compound Solution for a TO Film

0.701 g of tin (IV) chloride pentahydrate was dissolved in 10 ml ofethanol, yielding a TO film raw material compound solution.

Using this ITO film raw material compound solution and this TO film rawmaterial compound solution, and employing the same sequence as theexample 1, an ITO film of thickness 420 nm and a TO film of thickness160 nm were formed on a heat resistant glass plate, yielding atransparent electrode plate according to the present invention.

For the purposes of comparison, identical heat resistant glass platesand the same operations were used to form a transparent electrode platecomprising only an ITO film of thickness 420 nm, and a transparentelectrode plate comprising only a TO film of thickness 160 nm.

These three different types of transparent electrode plate were placedin a heating furnace and heated, either at 450° C. for one hour in air,or at 450° C. for 2 two hours in air, and the variation in the sheetresistance, the specific resistivity, and the transparency were thenevaluated. Measurements of electrical resistance were performed usingthe four terminal method, and measurements of transparency wereperformed using an ultraviolet-visible spectrophotometer at wavelengthsof 500 nm and 600 nm.

The results are shown in Table 7 through Table 9. Table 7 shows the dataprior to heating, Table 8 shows the data for the transparent electrodeplate following heating at 450° C. for one hour in air, and Table 9shows the data for the transparent electrode plate following heating at450° C. for two hours in air.

TABLE 7 Sheet Film Specific Transmittance Transmittance resistancethickness resistivity at 500 nm at 600 nm (Ω/□) (nm) (Ω · cm) (%) (%)ITO film 4.0 420 1.7 × 10⁻⁴ 86 95 TO film 5.8 × 10² 160 9.3 × 10⁻³ 85 98TO and 5.6 580 3.3 × 10⁻⁴ 82 96 ITO films

TABLE 8 Sheet Film Specific Transmittance Transmittance resistancethickness resistivity at 500 nm at 600 nm (Ω/□) (nm) (Ω · cm) (%) (%)ITO film 17 420 7.1 × 10⁻⁴ 88 95 TO film 9.7 × 10² 160 1.6 × 10⁻² 87 98TO and 6.6 580 3.8 × 10⁻⁴ 83 96 ITO films

TABLE 9 Sheet Film Specific Transmittance Transmittance resistancethickness resistivity at 500 nm at 600 nm (Ω/□) (nm) (Ω · cm) (%) (%)ITO film 18 420 7.6 × 10⁻⁴ 88 95 TO film 1.1 × 10³ 160 1.8 × 10⁻² 87 97TO and 6.9 580 4.0 × 10⁻⁴ 84 96 ITO films

From the results shown in Table 4 through Table 9 it is evident that,even if an ATO film or a TO film is laminated on top of the ITO filminstead of the FTO film, essentially the same results can be obtained.

Example 4

Using the same raw material compound solution for an ITO film and rawmaterial compound solution for a FTO film as in Example 1, a transparentelectrode plate was obtained by carrying out a film formation operationusing the same SPD method, forming an ITO film having a thickness of 450nm on heat resistant glass (CORNING #7059, 10 mm×10 mm×1.1 mm), andforming 9 different types of FTO films having thicknesses of 0-350 nmthereon.

These 9 types of transparent electrode plates were heated in a heatingfurnace at temperatures between 250-700° C. for one hour in air, and thesheet resistance after film forming and the sheet resistance afterheating were measured.

The results are shown in Table 10.

TABLE 10 Sheet resistance Sheet resistance Sheet resistance Sheetresistance Sheet resistance Sheet resistance Film thickness during filmafter one hour at after one hour at after one hour at after one hour atafter one hour at of FTO film forming 250° C. 300° C. 450° C. 650° C.700° C. (nm) (Ω/□) (Ω/□) (Ω/□) (Ω/□) (Ω/□) (Ω/□) 0 4.2 6.9 10.2 18.518.6 18.6 30 4.0 4.0 4.0 4.5 10.4 15.5 60 4.0 4.0 4.0 4.1 9.6 12.3 1004.3 4.3 4.3 4.3 6.0 9.1 150 3.8 3.8 3.8 3.8 4.5 5.5 200 3.9 3.9 3.9 3.94.2 4.9 250 3.8 3.8 3.8 3.8 4.1 4.7 300 3.9 3.9 3.9 3.9 4.0 4.5 350 4.04.0 4.0 4.0 4.0 4.2

It can be understood from the results of Table 10 that in order toobtain a transparent electrode plate whose conductivity does notdecrease even if heated at 250° C. for one hour in air, for example, thethickness of the FTO film may be set to 30 nm, and in order to obtain atransparent electrode plate whose conductivity does not decrease even ifheated at 700° C. for one hour in air, the thickness of the FTO film maybe set to a minimum of 150 nm.

Example 5

Using the same raw material compound solution for an ITO film and rawmaterial compound solution for a FTO film as in Example 1, a transparentelectrode plate was obtained by carrying out a film formation operationusing the same SPD method, forming 8 different types of ITO film havingthicknesses of 100-1400 nm on heat resistant glass (Corning #7059, 10mm×10 mm×1.1 mm), and forming a FTO film having a thickness of 150 nmthereon.

The sheet resistance after film forming and the light transmittance (550nm wavelength, absorption of heat resistant glass plate of the substratewas subtracted) of these 8 types of transparent electrode plates weremeasured. The sheet resistance of the transparent electrode plates afterheating at 450° C. for one hour in air was also measured.

The results are shown in Table 11.

TABLE 11 ITO film Sheet resistance Sheet resistance after Transmittancethickness during film forming one hour at 450° C. (550 nm) (nm) (Ω/□)(Ω/□) (%) 100 13.5 13.5 97 200 7.0 7.0 96 400 4.8 4.8 95 600 2.3 2.3 91800 1.5 1.5 89 1000 1.3 1.3 81 1200 1.0 1.0 76 1400 0.79 0.79 70

It can be understood from the results of Table 11 that if the thicknessof the ITO film exceeds 1000 nm, the light transmittance begins todecrease. Furthermore, it can be understood that if a FTO film havingthe required thickness is present and is coated, there is absolutely noeffect on the heat resistance thereof even if the film thickness of theITO film is varied.

Example 6 1. Preparation of Raw Material Compound Solution for an ITOFilm

3.33 g of indium chloride (III) tetrahydrate and 0.135 g of tin chloride(II) dihydrate were dissolved in 60 ml of ethanol, thereby producing theraw material compound solution for an ITO film.

2. Preparation of Raw Material Compound Solution for a FTO Film

0.701 g of tin chloride (IV) pentahydrate was dissolved in 10 ml ofethanol. 0.592 g of a saturated aqueous solution of ammonium fluoridewas added thereto. This mixture was placed in an ultrasonic washer forabout 20 minutes and completely dissolved, thereby producing the rawmaterial compound solution for a FTO film.

Using this raw material compound solution for an ITO film and rawmaterial compound solution for a FTO film, a transparent electrode platewas obtained by carrying out a film formation operation using the sameSPD method as in Example 1, forming 13 types of ITO film on heatresistant glass (Corning #7059, 10 mm×10 mm×1.1 mm) by varying the filmformation temperature from 220-460° C., and subsequently forming a FTOfilm thereon at a film formation temperature of 400° C.

These 13 types of transparent electrode plates were heated in a heatingfurnace at 450° C. for one hour in air, and the sheet resistance andspecific resistance after film forming as well as the sheet resistance,specific resistance, and transmittance after heating were measured.

The results are shown in Table 12.

TABLE 12 Specific Film formation Sheet resistance Specific Sheetresistance resistance after temperature of during film resistance duringafter one hour at one hour at Transmittance ITO film forming Filmthickness film forming 450° C. 450° C. (550 nm) (° C.) (Ω/□) (nm) (Ω ·cm) (Ω/□) (Ω/□) (%) 220 181 300 5.4 × 10⁻³ 181 5.4 × 10⁻³ 96 240 30.6480 1.4 × 10⁻³ 30.6 1.4 × 10⁻³ 95 260 11.2 500 5.7 × 10⁻⁴ 11.2 5.7 ×10⁻⁴ 94 280 3.5 600 2.1 × 10⁻⁴ 3.5 2.1 × 10⁻⁴ 93 300 3.1 680 2.1 × 10⁻⁴3.1 2.1 × 10⁻⁴ 92 320 3.0 720 2.2 × 10⁻⁴ 3.0 2.2 × 10⁻⁴ 92 340 2.7 7802.0 × 10⁻⁴ 2.7 2.0 × 10⁻⁴ 91 360 2.4 830 2.0 × 10⁻⁴ 2.4 2.0 × 10⁻⁴ 90380 2.0 950 1.9 × 10⁻⁴ 2.0 1.9 × 10⁻⁴ 88 400 1.8 1000 1.8 × 10⁻⁴ 1.8 1.8× 10⁻⁴ 87 420 1.6 1100 1.8 × 10⁻⁴ 1.6 1.8 × 10⁻⁴ 83 440 1.5 1200 1.8 ×10⁻⁴ 1.5 1.8 × 10⁻⁴ 81 460 1.3 1350 1.8 × 10⁻⁴ 1.3 1.8 × 10⁻⁴ 78

It is clear from the results of Table 12 that when the film formationtemperature of the ITO film is 280-460° C., it is possible to form alow-resistance transparent electrode film.

Example 7 1. Preparation of Raw Material Compound Solution for an ITOFilm

3.33 g of indium chloride (III) tetrahydrate and 0.135 g of tin chloride(II) dihydrate were dissolved in 60 ml of ethanol, thereby producing theraw material compound solution for an ITO film.

2. Preparation of Raw Material Compound Solution for a FTO Film

0.20 M of tin chloride (IV) pentahydrate was dissolved in ethanol. 0.32M of a saturated aqueous solution of ammonium fluoride was addedthereto. This mixture was placed in an ultrasonic washer for about 20minutes and completely dissolved, thereby producing the raw materialcompound solution for a FTO film.

Using this raw material compound solution for an ITO film and rawmaterial compound solution for a FTO film, a transparent electrode platewas obtained by carrying out a film formation operation using the sameSPD method as in Example 1, forming an ITO film (thickness: 570 nm) onheat resistant glass (Corning #7059, 10 mm×10 mm×1.1 mm) at a filmformation temperature of 350° C., and subsequently forming 12 types ofFTO film (thickness: 180 nm) thereon by varying the film formationtemperature from 240-460° C.

These 12 types of transparent electrode plates were heated in a heatingfurnace at 450° C. for one hour in air, and the sheet resistance andspecific resistance after film forming as well as the sheet resistance,specific resistance, and transmittance after heating were measured.

The results are shown in Table 13.

TABLE 13 Specific Film formation Sheet resistance Specific Sheetresistance resistance after temperature of during film resistance duringafter one hour at one hour at Transmittance FTO film forming Filmthickness film forming 450° C. 450° C. (550 nm) (° C.) (Ω/□) (nm) (Ω ·cm) (Ω/□) (Ω/□) (%) 240 2.6 750 2.0 × 10⁻⁴ 5.0 3.8 × 10⁻⁴ 89 260 2.6 7502.0 × 10⁻⁴ 4.8 3.6 × 10⁻⁴ 88 280 2.6 750 2.0 × 10⁻⁴ 4.8 3.6 × 10⁻⁴ 89300 2.6 750 2.0 × 10⁻⁴ 4.8 3.6 × 10⁻⁴ 87 320 2.6 750 2.0 × 10⁻⁴ 4.8 3.6× 10⁻⁴ 88 340 2.6 750 2.0 × 10⁻⁴ 3.5 2.6 × 10⁻⁴ 88 360 2.6 750 2.0 ×10⁻⁴ 2.8 2.1 × 10⁻⁴ 89 380 2.6 750 2.0 × 10⁻⁴ 2.6 2.0 × 10⁻⁴ 87 400 2.6750 2.0 × 10⁻⁴ 2.6 2.0 × 10⁻⁴ 89 420 2.6 750 2.0 × 10⁻⁴ 2.6 2.0 × 10⁻⁴88 440 2.6 750 2.0 × 10⁻⁴ 2.9 2.2 × 10⁻⁴ 88 460 2.6 750 2.0 × 10⁻⁴ 3.42.6 × 10⁻⁴ 86

It can be understood from the results of Table 13 that by setting thefilm formation temperature of the FTO film 3 to 360-440° C., atransparent electrode layer having excellent heat resistance can beformed while maintaining low resistance even after heating at 450° C.for one hour in air.

1.-12. (canceled)
 13. A method of producing a substrate for atransparent electrode, comprising forming an indium tin oxide film on atransparent substrate at 280° C. or higher by means of a spray pyrolysisdeposition method and forming a fluorine doped tin oxide film on theindium tin oxide film.
 14. A method of producing a substrate for atransparent electrode, comprising forming an indium tin oxide film on atransparent substrate by means of a spray pyrolysis deposition methodand forming a fluorine doped tin oxide film on the indium tin oxide filmat a temperature of about 360 to about 440° C.
 15. A photoelectricconversion element comprising a substrate for a transparent electrodeaccording to claim 1 as a transparent electrode plate.
 16. Aphotoelectric conversion element comprising a substrate for atransparent electrode according to claim 2 as a transparent electrodeplate.
 17. A dye sensitized solar cell comprising a substrate for atransparent electrode according to claim 1 as a transparent electrodeplate.
 18. A dye sensitized solar cell comprising a substrate for atransparent electrode according to claim 2 as a transparent electrodeplate.
 19. A photoelectric conversion element comprising a substrate fora transparent electrode according to claim 7 as a transparent electrodeplate.
 20. A dye sensitized solar cell comprising a substrate for atransparent electrode according to claim 7 as a transparent electrodeplate.
 21. A photoelectric conversion element comprising a substrate fora transparent electrode according to claim 8 as a transparent electrodeplate.
 22. A dye sensitized solar cell comprising a substrate for atransparent electrode according to claim 8 as a transparent electrodeplate.
 23. A photoelectric conversion element comprising a substrate fora transparent electrode according to claim 9 as a transparent electrodeplate.
 24. A dye sensitized solar cell comprising a substrate for atransparent electrode according to claim 9 as a transparent electrodeplate.
 25. A photoelectric conversion element comprising a substrate fora transparent electrode according to claim 10 as a transparent electrodeplate.
 26. A dye sensitized solar cell comprising a substrate for atransparent electrode according to claim 10 as a transparent electrodeplate.